chore(common): add support for start script

Author: nickchecan

Makefile

@@ -1,4 +1,4 @@
-APP_DIR := test/my-app
+APP_DIR := test/my-app-1
 BUILD_DIR := /tmp/uv-bp-build
 CACHE_DIR := /tmp/uv-bp-cache
 ENV_DIR := /tmp/uv-bp-env
@@ -24,4 +24,15 @@ test-buildpack: clean-test-buildpack
 
 # Start the staged sample app locally using the dependencies prepared by `test-buildpack`.
 start-local:
-	cd $(BUILD_DIR) && /bin/bash -lc 'source .profile.d/python.sh && $(PYTHON_BIN) main.py'
+	@cd $(BUILD_DIR) && /bin/bash -lc '\
+		source .profile.d/python.sh && \
+		if [ -f Procfile ]; then \
+			WEB_CMD=$$(awk -F": " '\''$$1 == "web" { print $$2; exit }'\'' Procfile); \
+		else \
+			WEB_CMD=$$($(BUILDPACK_DIR)/bin/release | awk -F": " '\''$$1 ~ /web/ { print $$2; exit }'\''); \
+		fi; \
+		if [ -z "$$WEB_CMD" ]; then \
+			echo "Could not determine a web command to run locally."; \
+			exit 1; \
+		fi; \
+		eval "$$WEB_CMD"'

bin/compile

@@ -35,20 +35,29 @@ if [ -f "pyproject.toml" ] && [ -f "uv.lock" ]; then
   PYTHON_VERSION=$("$PYTHON_BIN" -c 'import sys; print(f"{sys.version_info.major}.{sys.version_info.minor}")')
   # Stage dependencies into a buildpack-owned location instead of a local venv.
   SITE_PACKAGES_DIR="$BUILD_DIR/.python_packages/lib/python${PYTHON_VERSION}/site-packages"
+  SRC_DIR="$BUILD_DIR/src"
   PROFILE_DIR="$BUILD_DIR/.profile.d"
   EXPORT_FILE="$BUILD_DIR/.uv-export-requirements.txt"
 
   mkdir -p "$SITE_PACKAGES_DIR" "$PROFILE_DIR"
 
   # Export the exact locked dependency set from uv, then install those
   # packages into the staged site-packages directory.
-  uv export --locked --format requirements-txt -o "$EXPORT_FILE"
+  uv export --locked --format requirements-txt --no-emit-local -o "$EXPORT_FILE"
   "$PYTHON_BIN" -m pip install --no-deps --target "$SITE_PACKAGES_DIR" -r "$EXPORT_FILE"
 
   # Add the staged packages to PYTHONPATH so the app can import them at runtime.
-  cat > "$PROFILE_DIR/python.sh" <<EOF
+  # If the project uses a `src/` layout, include that too because the local
+  # project itself is not installed by the exported third-party requirements.
+  if [ -d "$SRC_DIR" ]; then
+    cat > "$PROFILE_DIR/python.sh" <<EOF
+export PYTHONPATH="$SRC_DIR:$SITE_PACKAGES_DIR:\${PYTHONPATH}"
+EOF
+  else
+    cat > "$PROFILE_DIR/python.sh" <<EOF
 export PYTHONPATH="$SITE_PACKAGES_DIR:\${PYTHONPATH}"
 EOF
+  fi
 else
   echo "No supported uv project found. Expected both pyproject.toml and uv.lock."
   exit 1

bin/release

@@ -1,16 +1,50 @@
 #!/usr/bin/env bash
 # Release script for Python buildpack with uv support
 
+if command -v python3 >/dev/null 2>&1; then
+  PYTHON_BIN="python3"
+elif command -v python >/dev/null 2>&1; then
+  PYTHON_BIN="python"
+else
+  PYTHON_BIN="python"
+fi
+
 # If the app provides its own Procfile, let Cloud Foundry use that.
 if [ -f "Procfile" ]; then
   exit 0
-# Otherwise, choose a reasonable default entrypoint based on common app files.
+# Otherwise, prefer a `start` entry under `[project.scripts]` in pyproject.toml.
+elif [ -n "$PYTHON_BIN" ] && [ -f "pyproject.toml" ]; then
+  START_TARGET=$("$PYTHON_BIN" -c '
+import sys
+try:
+    import tomllib
+except ModuleNotFoundError:
+    import tomli as tomllib
+
+with open("pyproject.toml", "rb") as f:
+    data = tomllib.load(f)
+
+print(data.get("project", {}).get("scripts", {}).get("start", ""))
+')
+
+  if [ -n "$START_TARGET" ]; then
+    MODULE_NAME="${START_TARGET%%:*}"
+    FUNCTION_NAME="${START_TARGET##*:}"
+    DEFAULT_WEB_PROCESS="${PYTHON_BIN} -c \"from ${MODULE_NAME} import ${FUNCTION_NAME}; ${FUNCTION_NAME}()\""
+  elif [ -f "main.py" ]; then
+    DEFAULT_WEB_PROCESS="${PYTHON_BIN} main.py"
+  elif [ -f "app.py" ]; then
+    DEFAULT_WEB_PROCESS="${PYTHON_BIN} app.py"
+  else
+    DEFAULT_WEB_PROCESS="${PYTHON_BIN} -m uvicorn main:app --host 0.0.0.0 --port \${PORT:-8000}"
+  fi
+# If pyproject.toml is missing or cannot be parsed here, fall back to common app files.
 elif [ -f "main.py" ]; then
-  DEFAULT_WEB_PROCESS="python main.py"
+  DEFAULT_WEB_PROCESS="${PYTHON_BIN} main.py"
 elif [ -f "app.py" ]; then
-  DEFAULT_WEB_PROCESS="python app.py"
+  DEFAULT_WEB_PROCESS="${PYTHON_BIN} app.py"
 else
-  DEFAULT_WEB_PROCESS="python -m uvicorn main:app --host 0.0.0.0 --port \${PORT:-8000}"
+  DEFAULT_WEB_PROCESS="${PYTHON_BIN} -m uvicorn main:app --host 0.0.0.0 --port \${PORT:-8000}"
 fi
 
 cat <<EOF